The present invention relates to an error compensation arrangement for a length or angle measuring instrument, of the type which includes a base and a measuring scale positioned on the base.
West German DE-OS No. 32 24 005 discloses a measuring scale which defines recesses in which elements are engaged in order to apply varied longitudinal tensions to the measuring scale. This measuring scale is a closed system in itself, because the tension-producing elements are mounted directly to the scale. After the measuring scale has been corrected outside of the measuring system, it can then be installed in the measuring system in a balanced, corrected state.
In addition, a number of error compensating arrangements of past measuring systems have been devised in which the adjusting devices for the compensation of errors are mounted to react against a base. These adjusting devices operate to vary the effective length of the measuring scale.
For example, German patent DE-PS No. 25 18 745 includes adjusting devices for applying tensile or compressive forces to the face sides of the measuring scale in order to stretch or compress this measuring scale uniformly along its entire length. In this way, linear errors are compensated. The measuring scale in this patent is relatively rigid and resistant to bending.
German DE-AS No. 27 35 154 discloses an arrangement for compensating non-linear errors by deflecting a measuring scale perpendicularly to the plane of the graduation. The bending of the measuring graduation leads to effective elongations or compressions at the region of deflection, since the edge zones of the measuring scale at the surface at which the measuring graduation is located are altered in effective length.
Each of these arrangements has its own disadvantages. Thus, the system disclosed in DE-PS No. 25 18 745 can only be used to compensate for linear errors. The system disclosed in DE-AS No. 27 35 154 results in a measuring scale which is relatively difficult to scan, since the scale has been deflected perpendicularly to the graduation plane and the scanning distance is therefore variable.
This last mentioned disadvantage can be avoided according to FIG. 4 of DE-AS No. 27 35 154 by directly guiding the scanning unit on the scale. However, this approach requires a relatively expensive coupling of the scanning unit to the object to be measured, since the scanning unit is not guided on a flat surface.